In our previous studies of the folding mechanism of cytochrome c using complementary fragments, we have shown (by means of stopped-flow techniques), that it is possible to resolve the complementaton (folding) process into consecutive kinetic events and to identify some of the structural changes associated with those events. These experiments were performed at a constant temperature, 25 degrees C. We have now completed a study of the temperature dependence of the rate constants (both forward and reverse) for the complementation of heme fragment (1-25)H with apofragment (23-104)(productive complex) and with apofragment (39-104)(nonproductive complex). Equilibrium data for the thermal unfolding of these complexes have also been determined. Utilizing both types of data, activation parameters for the various transition states as well as apparent changes in the standard thermodynamic functions accompanying each kinetic phase have been estimated. A temperature jump study of the reactions involving ligation of methionine 80 to the heme iron in native cytochrome c as well as in a productive fragment complex has also been completed.